1. Field of the Invention
The present invention is directed to an electrical resistor having a substrate with a layer of metal or metal alloy in which carbon has been inserted to vary the temperature coefficient of the electrical resistance and the specific resistance and to the method of producing the electrical resistor.
2. Prior Art
Resistance layers comprising a metal component such as a metal or a metal alloy with carbon inserted therein are well-known in the prior art. One proposed method for producing such resistors is by evaporating the metal of the resistance layer onto a substrate by a process using an electron beam to evaporate either tungsten or molybdenum respectively in the presence of a carbon containing gas. Due to the reaction occurring during evaporation, carbon is supposed to influence the temperature coefficient of the electrical resistor. Such a process is disclosed in the German Offenlegungsschrift No. 1,931,412. Two drawbacks of this process is that the method is time consuming and the apparatus for performing the method is extremely expensive.
Another method involves a pyrolytic decomposition of a metal-organic compound dissolved in a solution by submerging a heated substrate, which receives the layer, in the solution. In this process, which is described in German Offenlegungsschrift No. 1,540,166, the metal matrix of the layer may contain between 1 and 15 volume percent carbon. However, this method has several drawbacks. During the pyrolytic decomposition of the metal-organic compound, it is difficult to maintain the concentration of the compound in the solution. Another drawback is the fact that only a maximum of 15 volume percent of carbon can be introduced into the metal or metal alloy matrix.
Resistors, which comprise a layer on a substrate and have a high resistance, are known. They were produced by either reducing the layer thickness of the resistance layer or by a corresponding selection of the geometric factors of the resistor layers. The electrical characteristics of the layer could be changed by a diffusion process or by a corrosion process. However, since the composition of the resistance layer comprises an essential portion of the entire layer, particularly in very thin resistance layers (5 to 10nm or 50 or 100 angstroms), the changing of the layer thickness or geometric factors by the above process involves a great danger of undesirably changing the electrical properties of the resistor due to minor changes in the composition of the layers.